In 1885 Hermann Ebbinhaus discovered the exponential nature of forgetting and published his findings in "Über das Gedächtnis" ("Memory: A Contribution to Experimental Psychology").
The rate at which learned material is forgotten depends on how meaningful it is, and on spacing of its repetition. It therefore follows that the return on trade publication advertising is directly related to the degree to which an advertisement appeals to the self interest of a
reader, and the frequency at which the reader is exposed to repeat insertions.
Repeating your advertisements before prior insertions are forgotten, continually increases the average recall and recognition of your products and your company. This yields greater awareness, preference and return on investment — and drives more traffic to your website — than the same number of ads placed erratically.